Nice, it's always good to have options!!
I am currently using mEdit - http://kthx.net/medit/
mEdit.dll gives me syntax highlight right on mIRC Editor, along with NoInstaCrash.dll (because some people say mEdit.dll is instable and crashes mIRC often) ...
I had tried both dlls, noinstacrash.dll when the mirc is crashing it causing some problems to prevent the crash, and medit.dll was having a lot of bugs according large files and fonting issues.
Have a try in msldev.com that is more stable but is also outdated.